U.S. patent application number 14/844478 was filed with the patent office on 2016-03-10 for magnetic compound and method of producing the same.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Masaaki ITO, Akira KATO, Hidefumi KISHIMOTO, Kurima KOBAYASHI, Akira MANABE, Noritsugu SAKUMA, Shunji SUZUKI, Kota WASHIO, Masao YANO.
Application Number | 20160071635 14/844478 |
Document ID | / |
Family ID | 54106207 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160071635 |
Kind Code |
A1 |
SAKUMA; Noritsugu ; et
al. |
March 10, 2016 |
MAGNETIC COMPOUND AND METHOD OF PRODUCING THE SAME
Abstract
Provided is a magnetic compound represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e (wherein R represents one or more rare earth elements, T
represents one or more elements selected from the group consisting
of Ti, V, Mo, and W, M represents one or more elements selected
from the group consisting of unavoidable impurity elements, Al, Cr,
Cu, Ga, Ag, and Au, A represents one or more elements selected from
the group consisting of N, C, H, and P, 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.0.6, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c<7, 0.ltoreq.d.ltoreq.1, and 1.ltoreq.e.ltoreq.18), in
which a main phase of the magnetic compound includes a ThMn.sub.12
type crystal structure, and a volume percentage of an
.alpha.-(Fe,Co) phase is 20% or lower.
Inventors: |
SAKUMA; Noritsugu;
(Mishima-shi, JP) ; KATO; Akira; (Mishima-shi,
JP) ; WASHIO; Kota; (Sunto-gun, JP) ;
KISHIMOTO; Hidefumi; (Susono-shi, JP) ; YANO;
Masao; (Sunto-gun, JP) ; MANABE; Akira;
(Miyoshi-shi, JP) ; ITO; Masaaki; (Susono-shi,
JP) ; SUZUKI; Shunji; (Iwata-shi, JP) ;
KOBAYASHI; Kurima; (Fukuroi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
54106207 |
Appl. No.: |
14/844478 |
Filed: |
September 3, 2015 |
Current U.S.
Class: |
252/62.51R ;
148/101 |
Current CPC
Class: |
H01F 1/0593 20130101;
C22C 30/00 20130101; C22C 38/00 20130101; C22C 1/02 20130101; C22C
30/02 20130101 |
International
Class: |
H01F 1/03 20060101
H01F001/03; C22C 30/02 20060101 C22C030/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 9, 2014 |
JP |
2014-183705 |
May 12, 2015 |
JP |
2015-097526 |
Claims
1. A magnetic compound represented by
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e, the magnetic compound comprising a ThMn.sub.12 type crystal
structure, wherein a volume percentage of an .alpha.-(Fe,Co) phase
is 20% or lower, R represents one or more rare earth elements, T
represents one or more elements selected from the group consisting
of Ti, V, Mo, and W, M represents one or more elements selected
from the group consisting of unavoidable impurity elements, Al, Cr,
Cu, Ga, Ag, and Au, A represents one or more elements selected from
the group consisting of N, C, H, and P, 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.0.6, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c<7, 0.ltoreq.d.ltoreq.1, and 1.ltoreq.e.ltoreq.18.
2. The magnetic compound according to claim 1, wherein
0.ltoreq.x.ltoreq.0.3, and 7.ltoreq.e.ltoreq.14.
3. The magnetic compound according to claim 1, wherein a region
surrounded by 0<c<7, x.gtoreq.0, c>-38x+3.8 and
c>6.3x+0.65 is satisfied.
4. A method of producing the magnetic compound according to claim
1, the method comprising: a step of preparing molten alloy having a
composition represented by
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.d;
a step of quenching the molten alloy at a rate of 1.times.10.sup.2
K/sec to 1.times.10.sup.7 K/sec; and a step of crushing solidified
alloy, which is obtained by the quenching, and then causing A to
penetrate into the crushed alloy, wherein R represents one or more
rare earth elements, T represents one or more elements selected
from the group consisting of Ti, V, Mo, and W, M represents one or
more elements selected from the group consisting of unavoidable
impurity elements, Al, Cr, Cu, Ga, Ag, and Au,
0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.0.6, 4.ltoreq.a.ltoreq.20,
b=100-a-c-d, 0<c<7, 0.ltoreq.d.ltoreq.1, and A represents one
or more elements selected from the group consisting of N, C, H, and
P.
5. The method according to claim 4, further comprising: a step of
performing a heat treatment at 800.degree. C. to 1300.degree. C.
for 2 hours to 120 hours after the quenching step.
6. A rare earth element-containing magnetic compound comprising a
ThMn.sub.12 type crystal structure, wherein a lattice constant a of
the crystal structure is within a range of 0.850 nm to 0.875 nm, a
lattice constant c of the crystal structure is within a range of
0.480 nm to 0.505 nm, a lattice volume of the crystal structure is
within a range of 0.351 nm.sup.3 to 0.387 nm.sup.3, a hexagon A is
defined as a six-membered ring centering on a rare earth atom,
which is formed of Fe (8i) and Fe(8j) sites, a hexagon B is defined
as a six-membered ring which includes Fe (8i) and Fe(8j) sites in
which Fe (8i)-Fe (8i) dumbbells form two sides facing each other, a
hexagon C is defined as a six-membered ring which is formed of Fe
(8j) and Fe(8f) sites and whose center is positioned on a straight
line connecting Fe (8i) and the rare earth atom to each other, a
length of the hexagon A in a direction of axis a is shorter than
0.611 nm, an average distance between Fe (8i) and Fe (8i) in the
hexagon A is 0.254 nm to 0.288 nm, an average distance between Fe
(8j) and Fe (8j) in the hexagon B is 0.242 nm to 0.276 nm, and an
average distance between Fe (8f) and Fe (8f) facing each other with
the center of the hexagon C interposed therebetween in the hexagon
C is 0.234 nm to 0.268 nm.
7. A magnetic powder which is made of a compound represented by
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e, the magnetic powder comprising a ThMn.sub.12 type crystal
structure, wherein a volume percentage of an .alpha.-(Fe,Co) phase
is 20% or lower, R represents one or more rare earth elements, T
represents one or more elements selected from the group consisting
of Ti, V, Mo, and W, M represents one or more elements selected
from the group consisting of unavoidable impurity elements, Al, Cr,
Cu, Ga, Ag, and Au, A represents one or more elements selected from
the group consisting of N, C, H, and P, 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.0.7, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c.ltoreq.7, 0.ltoreq.d.ltoreq.1, and 1.ltoreq.e.ltoreq.18.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2014-183705 and 2015-097526 filed on Sep. 9, 2014 and May 12, 2015
including the specification, drawings and abstract is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetic compound having
a ThMn.sub.12 type crystal structure with high anisotropy field and
high saturation magnetization, and a method of producing the
same.
[0004] 2. Description of Related Art
[0005] The application of a permanent magnet has been spread in a
wide range of fields including electronics, information and
telecommunications, medical cares, machine tools, and industrial
and automotive motors, and the demand for reduction in the amount
of carbon dioxide emissions has increased. In such a situation,
development of a high-performance permanent magnet has been
increasingly expected along with the spread of hybrid vehicles,
energy-saving in industrial fields, the improvement of power
generation efficiency, and the like.
[0006] A Nd--Fe--B magnet which is currently predominant in the
market as a high-performance magnet is used as a magnet for a drive
motor of a HV/EHV. Recently, it has been required to further reduce
the size of a motor and to further increase the output of a motor
(to increase the residual magnetization of a magnet). Accordingly,
the development of a new permanent magnet material has been
progressing.
[0007] In order to develop a material having higher performance
than a Nd--Fe--B magnet, a study regarding a rare earth
element-iron magnetic compound having a ThMn.sub.12 type crystal
structure has been carried out. For example, Japanese Patent
Application Publication No. 2004-265907 (JP 2004-265907 A) proposes
a hard magnetic composition which is represented by
R(Fe.sub.100-y-wCo.sub.wTi.sub.y).sub.xSi.sub.zA.sub.v (wherein R
represents one element or two or more elements selected from rare
earth elements including Y in which Nd accounts for 50 mol % or
higher of the total amount of R; A represents one element or two
elements of N and C; x=10 to 12.5; y=(8.3-1.7.times.z) to 12; z=0.2
to 2.3; v=0.1 to 3; and w=0 to 30) and has a single-layer structure
of a phase having a ThMn.sub.12 type crystal structure.
[0008] In the currently proposed compound which has a
NdFe.sub.11TiN.sub.x composition having a ThMn.sub.12 type crystal
structure, anisotropy field is high; however, saturation
magnetization is lower than that of a Nd--Fe--B magnet and does not
reach the level of a magnet material.
SUMMARY OF THE INVENTION
[0009] The invention provides a magnetic compound having high
anisotropy field and high saturation magnetization at the same
time.
[0010] According to the first aspect of the invention, the
following configuration is provided. A magnetic compound
represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e (wherein R represents one or more rare earth elements, T
represents one or more elements selected from the group consisting
of Ti, V, Mo, and W, M represents one or more elements selected
from the group consisting of unavoidable impurity elements, Al, Cr,
Cu, Ga, Ag, and Au, A represents one or more elements selected from
the group consisting of N, C, H, and P, 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq..ltoreq.0.6, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c<7, 0.ltoreq.d.ltoreq.1, and 1.ltoreq.e.ltoreq.18), the
magnetic compound including a ThMn.sub.12 type crystal structure,
in which a volume percentage of an .alpha.-(Fe,Co) phase is 20% or
lower.
[0011] In the magnetic compound, 0.ltoreq.x.ltoreq.0.3, and
7.ltoreq.e.ltoreq.14 may be satisfied.
[0012] In the magnetic compound, in the formula, a relationship
between x and c may satisfy a region surrounded by 0<c<7,
x.gtoreq.0, c>-38x+3.8 and c>6.3x+0.65.
[0013] A method of producing the above-described magnetic compound
of the second aspect of the present invention, the method
including: a step of preparing molten alloy having a composition
represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.d
(wherein R represents one or more rare earth elements, T represents
one or more elements selected from the group consisting of Ti, V,
Mo, and W, M represents one or more elements selected from the
group consisting of unavoidable impurity elements, Al, Cr, Cu, Ga,
Ag, and Au, 0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.0.6,
4.ltoreq.a.ltoreq.20, b=100-a-c-d, 0<c<7, and
0.ltoreq.d.ltoreq.1); a step of quenching the molten alloy at a
rate of 1.times.10.sup.2 K/sec to 1.times.10.sup.7 K/sec; and a
step of crushing solidified alloy, which is obtained by the
quenching, and then causing A (A represents one or more elements
selected from the group consisting of N, C, H, and P) to penetrate
into the crushed alloy.
[0014] The method may include a step of performing a heat treatment
at 800.degree. C. to 1300.degree. C. for 2 hours to 120 hours after
the quenching step.
[0015] A rare earth element-containing magnetic compound of the
third aspect of the invention including a ThMn.sub.12 type crystal
structure, in which a lattice constant a of the crystal structure
is within a range of 0.850 nm to 0.875 nm, a lattice constant c of
the crystal structure is within a range of 0.480 nm to 0.505 nm, a
lattice volume of the crystal structure is within a range of 0.351
nm.sup.3 to 0.387 nm.sup.3, a hexagon A is defined as a
six-membered ring centering on a rare earth atom, which is formed
of Fe (8i) and Fe(8j) sites, a hexagon B is defined as a
six-membered ring which includes Fe (8i) and Fe(8j) sites in which
Fe (8i)-Fe (8i) dumbbells form two sides facing each other, a
hexagon C is defined as a six-membered ring which is formed of Fe
(8j) and Fe(8f) sites and whose center is positioned on a straight
line connecting Fe (8i) and a rare earth atom to each other, a
length of the hexagon A in a direction of axis a is shorter than
0.611 nm, an average distance between Fe (8i) and Fe (8i) in the
hexagon A is 0.254 nm to 0.288 nm, an average distance between Fe
(8j) and Fe (8j) in the hexagon B is 0.242 nm to 0.276 nm, and an
average distance between Fe (8f) and Fe (8f) facing each other with
the center of the hexagon C interposed therebetween in the hexagon
C is 0.234 nm to 0.268 nm.
[0016] A magnetic powder of the fourth aspect of the present
invention which is made of a compound represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e (wherein R represents one or more rare earth elements, T
represents one or more elements selected from the group consisting
of Ti, V, Mo, and W, M represents one or more elements selected
from the group consisting of unavoidable impurity elements, Al, Cr,
Cu, Ga, Ag, and Au, A represents one or more elements selected from
the group consisting of N, C, H, and P, 0.ltoreq.x.ltoreq.0.5,
0.ltoreq.y.ltoreq.0.7, 4.ltoreq.a.ltoreq.20, b=100-a-c-d,
0<c.ltoreq.7, 0.ltoreq.d.ltoreq.1, and 1.ltoreq.e.ltoreq.18),
the magnetic powder including a ThMn.sub.12 type crystal structure,
in which a volume percentage of an .alpha.-(Fe,Co) phase is 20% or
lower.
[0017] According to the invention, in the compound which includes a
ThMn.sub.12 type crystal structure and is represented by the
formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e, percentages of magnetic elements including Fe and Co can
increase and magnetization can be improved by reducing the T
content. In addition, the amount of an .alpha.-(Fe,Co) phase
deposited during cooling can be reduced by adjusting the cooling
rate of molten alloy during the production process, and
magnetization can be improved by depositing a large amount of a
ThMn.sub.12 type crystal. Further, a balance between the sizes of
the respective hexagons can be improved and a ThMn.sub.12 type
crystal structure can be stably obtained by adjusting the sizes of
the respective hexagons as defined above in (6).
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Features, advantages, and technical and industrial
significance of exemplary embodiments of the invention will be
described below with reference to the accompanying drawings, in
which like numerals denote like elements, and wherein:
[0019] FIG. 1 is a graph showing a stable region of T in an
RFe.sub.12-xT.sub.x compound;
[0020] FIG. 2 is a schematic diagram showing an apparatus used in a
strip casting method;
[0021] FIG. 3 is a perspective view schematically showing a
ThMn.sub.12 type crystal structure;
[0022] FIGS. 4A to 4C are perspective views schematically showing
hexagons A, B, and C in the ThMn.sub.12 type crystal structure;
[0023] FIGS. 5A and 5B are perspective views schematically showing
the hexagons A, B, and C in the ThMn.sub.12 type crystal
structure;
[0024] FIG. 6 is a perspective view schematically showing a change
in the size of the hexagons;
[0025] FIG. 7 is a table showing the compositions and
characteristics of magnets of Examples 1 to 5 and Comparative
Examples 1 to 5;
[0026] FIG. 8 is a graph showing the measurement results of
saturation magnetization (room temperature) and anisotropy field of
Examples 1 to 5 and Comparative Examples 1 to 5;
[0027] FIG. 9 is a graph showing the measurement results of
saturation magnetization (180.degree. C.) and anisotropy field of
Examples 1 to 5 and Comparative Examples 1 to 5;
[0028] FIG. 10 is a graph showing the measurement results of
saturation magnetization (room temperature) and anisotropy field of
Examples 6 and 7 and Comparative Examples 6 to 12;
[0029] FIG. 11 is a graph showing the measurement results of
saturation magnetization (180.degree. C.) and anisotropy field of
Examples 6 and 7 and Comparative Examples 6 to 12;
[0030] FIG. 12 is a table showing the compositions, production
methods, and characteristics of magnets of Examples 6 and 7 and
Comparative Examples 6 to 12;
[0031] FIG. 13 shows backscattered electron images of particles
obtained in Examples 6 and 7 and Comparative Example 8;
[0032] FIG. 14 is a graph showing the XRD results of the particles
obtained in Examples 6 and 7 and Comparative Example 8;
[0033] FIG. 15 is a graph showing a relationship between the size
of an .alpha.-(Fe,Co) phase in a sample before nitriding and the
volume percentage of the .alpha.-(Fe,Co) phase in the sample after
nitriding which are measured from an SEM image;
[0034] FIG. 16 is a table showing the compositions, Co substitution
ratios, and characteristics of magnets of Examples 8 to 15 and
Comparative Example 13;
[0035] FIG. 17 is a graph showing a relationship between a Co
substitution ratio and magnetic characteristics in each of Examples
8 to 15 and Comparative Example 13;
[0036] FIG. 18 is a graph showing a relationship between a Co
substitution ratio and magnetic characteristics in each of Examples
8 to 15 and Comparative Example 13;
[0037] FIG. 19 is a graph showing a relationship between a Co
substitution ratio and a Curie temperature in each of Examples 8 to
15 and Comparative Example 13;
[0038] FIG. 20 is a graph showing a relationship between a Co
substitution ratio and a lattice constant a of a crystal structure
in each of Examples 8 to 15 and Comparative Example 13;
[0039] FIG. 21 is a graph showing a relationship between a Co
substitution ratio and a lattice constant c of a crystal structure
in each of Examples 8 to 15 and Comparative Example 13;
[0040] FIG. 22 is a graph showing a relationship between a Co
substitution ratio and a lattice volume V in each of Examples 8 to
15 and Comparative Example 13;
[0041] FIG. 23 is a graph showing the measurement results of
saturation magnetization (room temperature) and anisotropy field of
Examples 8 to 15 and Comparative Example 13;
[0042] FIG. 24 is a graph showing the measurement results of
saturation magnetization (180.degree. C.) and anisotropy field of
Examples 8 to 15 and Comparative Example 13;
[0043] FIG. 25 is a table showing the compositions and
characteristics of magnets of Example 16 and Comparative Examples
14 to 17;
[0044] FIG. 26 is a table showing the Ti contents of magnets of
Example 16 and Comparative Examples 14 to 17;
[0045] FIG. 27 is a graph showing the XRD results of Example 16 and
Comparative Examples 14 to 17;
[0046] FIG. 28 is a table showing the compositions and
characteristics of magnets of Examples 17 to 23 and Comparative
Examples 18 to 25;
[0047] FIG. 29 is a table showing the compositions and
characteristics of magnets of Examples 24 to 27 and Comparative
Examples 26 to 31;
[0048] FIG. 30 is a graph showing a relationship between a Ti
content and a Zr change in each of Examples 17 to 27 and
Comparative Examples 18 to 31;
[0049] FIG. 31 is a table showing the compositions and
characteristics of magnets of Examples 28 to 33 and Comparative
Examples 32 and 33;
[0050] FIG. 32 is a graph showing a relationship between a N
content and a lattice constant a of a crystal structure in each of
Examples 28 to 33 and Comparative Examples 32 and 33;
[0051] FIG. 33 is a graph showing a relationship between a N
content and a lattice constant c of a crystal structure in each of
Examples 28 to 33 and Comparative Examples 32 and 33; and
[0052] FIG. 34 is a graph showing a relationship between a N
content and a lattice volume V in each of Examples 28 to 33 and
Comparative Examples 32 and 33.
DETAILED DESCRIPTION OF EMBODIMENTS
[0053] Hereinafter, a magnetic compound according to an embodiment
of the invention will be described in detail. The magnetic compound
according to the embodiment of the invention is represented by the
following formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e, and each component thereof will be described below.
[0054] R represents a rare earth element and is an essential
component in the magnetic compound according to the embodiment of
the invention to exhibit permanent magnet characteristics.
Specifically, R represents one or more elements selected from Y,
La, Ce, Pr, Nd, Sm, and Eu, and Pr, Nd, and Sm are preferably used.
A mixing amount a of R is 4 at % or higher and 20 at % or lower.
When the mixing amount a of R is lower than 4 at %, the deposition
of a Fe phase is great, and the volume percentage of the Fe phase
after a heat treatment cannot be decreased. When the mixing amount
a of R is higher than 20 at %, the amount of a grain boundary phase
is excessively large, and thus magnetization cannot be
improved.
[0055] Zr is efficient in stabilizing a ThMn.sub.12 type crystal
phase when substituted with a part of rare earth elements. That is,
Zr is substituted with R in the ThMn.sub.12 type crystal structure
to cause shrinkage of a crystal lattice. As a result, when the
temperature of an alloy becomes high or when a nitrogen atom or the
like is caused to penetrate into a crystal lattice, Zr has an
effect of stably maintaining the ThMn.sub.12 type crystal phase. On
the other hand, strong magnetic anisotropy derived from R is
weakened by Zr substitution from the viewpoint of magnetic
characteristics. Therefore, it is necessary to determine the Zr
content from the viewpoints of the stability and magnetic
characteristics of the crystal. However, in the embodiment of the
invention, Zr addition is not essential. When the Zr content is 0,
the ThMn.sub.12 type crystal phase can be stabilized, for example,
by adjusting the component composition of an alloy and performing a
heat treatment. Therefore, anisotropy field is improved. However,
when the amount of Zr substitution is more than 0.5, anisotropy
field significantly decreases. It is preferable that the Zr content
x satisfies 0.ltoreq.x.ltoreq.0.3.
[0056] T represents one or more elements selected from the group
consisting of Ti, V, Mo, and W. FIG. 1 is a graph showing a stable
region of T in an RFe.sub.12-xT.sub.x compound (source: K. H. J.
Buschow, Rep. Prog. Phys. 54, 1123 (1991)). It is known that the
ThMn.sub.12 type crystal structure is stabilized and superior
magnetic characteristics are exhibited by adding a third element
such as Ti, V, Mo, or W to an R--Fe binary alloy.
[0057] In the related art, the ThMn.sub.12 type crystal structure
is formed by adding a large amount of T exceeding the necessary
amount to obtain the stabilization effect of T. Therefore, the
content ratio of Fe constituting the compound in the alloy
decreases, and Fe atoms occupying sites, which have the largest
effect on magnetization, are replaced with, for example, Ti atoms,
thereby decreasing overall magnetization. In order to improve
magnetization, the mixing amount of Ti may be decreased. In this
case, however, the stabilization of the ThMn.sub.12 type crystal
structure deteriorates. In the related art, RFe.sub.11Ti is
reported as the RFe.sub.12-xTi.sub.x compound, but a compound in
which x is lower than 1, that is, Ti is lower than 7 at % has not
been reported.
[0058] When the amount of Ti which stabilizes the ThMm.sub.2 type
crystal structure is reduced, the stabilization of the ThMn.sub.12
type crystal structure deteriorates, and .alpha.-(Fe,Co) which
inhibits anisotropy field or coercive force is deposited. According
to the embodiment of the invention, the amount of .alpha.-(Fe,Co)
deposited can be suppressed by controlling the cooling rate of
molten alloy; and even when the mixing amount of T decreases, the
ThMn.sub.12 phase having high magnetic characteristics can be
stably formed by adjusting the volume percentage of an
.alpha.-(Fe,Co) phase in the compound to be a certain value or
lower.
[0059] The mixing amount of T is lower than 7 at % in which x in
the RFe.sub.12-xTi.sub.x compound is lower than 1. When the mixing
amount of Ti is 7 at % or higher, the content ratio of Fe
constituting the compound decreases, and overall magnetization
decreases.
[0060] In the compound according to the embodiment of the invention
represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e, it is preferable that a relationship between the Zr content x
and the T content c satisfies a region (0<c<7, x.gtoreq.0)
surrounded by c>-38x+3.8 and c>6.3x+0.65.
[0061] M represents one or more elements selected from the group
consisting of unavoidable impurity elements, Al, Cr, Cu, Ga, Ag,
and Au. The unavoidable impurity elements refer to elements
incorporated into raw materials or elements incorporated during the
production process, and specific examples thereof include Si and
Mn. M contributes to the inhibition of grain growth of the
ThMn.sub.12 type crystal and the viscosity and melting point of a
phase (for example, a grain boundary phase) other than the
ThMn.sub.12 type crystal but is not essential in the invention. A
mixing amount d of M is lower than 1 at %. When the mixing amount d
of M is higher than 1 at %, the content ratio of Fe constituting
the compound in the alloy decreases, and overall magnetization
decreases.
[0062] A represents one or more elements selected from the group
consisting of N, C, H, and P. A can be caused to penetrate into a
crystal lattice of the ThMn.sub.12 phase to expand the lattice in
the ThMn.sub.12 phase such that both characteristics of anisotropy
field and saturation magnetization can be improved. A mixing amount
e of A is 1 at % or higher and 18 at % or lower. When the mixing
amount e of A is lower than 1 at %, the effects cannot be
exhibited. When the mixing amount e of A is higher than 18 at %,
the content ratio of Fe constituting the compound in the alloy
decreases, a part of the ThMn.sub.12 phase is decomposed due to
deterioration in the stability of the ThMn12 phase, and overall
magnetization decreases. The mixing amount e of A is preferably
7.ltoreq.e.ltoreq.14.
[0063] A remainder of the compound according to the embodiment of
the invention other than the above-described elements is Fe, and a
part of Fe may be substituted with Co. Co can be substituted with
Fe to cause an increase in spontaneous magnetization according to
the Slater-Pauling rule such that both characteristics of
anisotropy field and saturation magnetization can be improved.
However, when the amount of Co substitution is higher than 0.6, the
effects cannot be exhibited. In addition, when Fe is substituted
with Co, the Curie point of the compound increases, and thus an
effect of suppressing a decrease in magnetization at a high
temperature can be obtained.
[0064] The magnetic compound according to the embodiment of the
invention is represented by the above-described formula and has a
ThMn.sub.12 type crystal structure. This ThMn.sub.12 type crystal
structure is tetragonal and shows peaks at 2.theta. values of
29.801.degree., 36.554.degree., 42.082.degree., 42.368.degree., and
43.219.degree. (.+-.0.5.degree.) in the XRD measurement results.
Further, in the magnetic compound according to the embodiment of
the invention, a volume percentage of an .alpha.-(Fe,Co) phase is
20% or lower. This volume percentage is calculated by embedding a
sample with a resin, polishing the sample, observing the sample
with OM or SEM-EDX, and obtaining an area ratio of the
.alpha.-(Fe,Co) phase in a cross-section by image analysis. Here,
when it is assumed that the structure is not randomly oriented, the
following relational expression of A.apprxeq.V is established
between the average area ratio A and the volume percentage V.
Therefore, in the embodiment of the invention, the area ratio of
the .alpha.-(Fe,Co) phase measured as described above is set as the
volume percentage.
[0065] As described above, in the magnetic compound according to
the embodiment of the invention, magnetization can be improved by
reducing the T content as compared to a RFe.sub.11Ti type compound
of the related art. In addition, both characteristics of anisotropy
field and saturation magnetization can be significantly improved by
reducing the volume percentage of the .alpha.-(Fe,Co) phase.
[0066] (Production Method)
[0067] Basically, the magnetic compound according to the embodiment
of the invention can be produced using a production method of the
related art such as a mold casting method or an arc melting method.
However, in the method of the related art, a large amount of the
stable phase (.alpha.-(Fe,Co) phase) other than the ThMn.sub.12 is
deposited, and anisotropy field and saturation magnetization
decrease. Here, focusing on the fact that a temperature at which
the ThMn.sub.12 type crystal is deposited is lower than a
temperature at which .alpha.-(Fe,Co) is deposited, in the
embodiment of the invention, molten alloy is quenched at a rate of
1.times.10.sup.2 K/sec to 1.times.10.sup.7 K/sec such that the
temperature of the molten alloy is prevented from being maintained
in a region near the temperature at which .alpha.-(Fe,Co) is
deposited for a long period of time. As a result, the deposition of
.alpha.-(Fe,Co) can be reduced and a large amount of the
ThMn.sub.12 type crystal can be produced.
[0068] As a cooling method, for example, molten alloy can be cooled
at a predetermined rate using an apparatus 10 shown in FIG. 2 and a
strip casting method. In the apparatus 10, alloy raw materials are
melted in a melting furnace 11 to prepare molten alloy 12 having a
composition represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.d.
In the above-described formula, T represents one or more elements
selected from the group consisting of Ti, V, Mo, and W, M
represents one or more elements selected from the group consisting
of unavoidable impurity elements, Al, Cr, Cu, Ga, Ag, and Au,
0.ltoreq.x.ltoreq.0.5, 0.ltoreq.y.ltoreq.0.6, 4.ltoreq.a.ltoreq.20,
b=100-a-c-d, 0<c<7, and 0.ltoreq.d.ltoreq.1. This molten
alloy 12 is supplied to a tundish 13 at a fixed supply rate. The
molten alloy 12 supplied to the tundish 13 is supplied to a cooling
roller 14 from an end of the tundish 13 due to its own weight.
[0069] Here, the tundish 13 is made of a ceramic, can temporarily
store the molten alloy 12 which is continuously supplied from the
melting furnace 11 at a predetermined flow rate, and can rectify
the flow of the molten alloy 12 to the cooling roller 14. In
addition, the tundish 13 has a function of adjusting the
temperature of the molten alloy 12 immediately before the molten
alloy 12 reaches the cooling roller 14.
[0070] The cooling roller 14 is formed of a material having high
thermal conductivity such as copper or chromium, and, for example,
the roller surface is plated with chromium to prevent corrosion
with the molten alloy having a high temperature. This roller can be
rotated by a drive device (not shown) at a predetermined rotating
speed in a direction indicated by an arrow. By controlling the
rotating speed, the cooling rate of the molten alloy can be
controlled to be 1.times.10.sup.2 K/sec to 1.times.10.sup.7
K/sec.
[0071] The molten alloy 12 which is cooled and solidified on the
outer periphery of the cooling roller 14 is peeled off from the
cooling roller 14 as flaky solidified alloy 15. The solidified
alloy 15 is crushed and collected by a collection device.
[0072] Further, the method according to the embodiment of the
invention may further include a step of performing a heat treatment
on particles obtained in the above-described step at 800.degree. C.
to 1300.degree. C. for 2 hours to 120 hours. Due to this heat
treatment, the ThMn.sub.12 phase is made to be homogeneous, and
both characteristics of anisotropy field and saturation
magnetization are further improved.
[0073] The collected alloy is crushed, and A (A represents one or
more elements selected from the group consisting of N, C, H, and P)
is caused to penetrate into the alloy. Specifically, when nitrogen
is used as A, the alloy is nitrided by performing a heat treatment
thereon using nitrogen gas or ammonia gas as a nitrogen source at a
temperature of 200.degree. C. to 600.degree. C. for 1 hour to 24
hours. When carbon is used as A, the alloy is carbonized by
performing a heat treatment thereon using C.sub.2H.sub.2 (CH.sub.4,
C.sub.3H.sub.8, or CO) gas or thermally decomposed gas of methanol
as a carbon source at a temperature of 300.degree. C. to
600.degree. C. for 1 hour to 24 hours. In addition, solid
carburizing using carbon powder or carburizing using molten salt
such as KCN or NaCN can be performed. In regard to H and P, typical
hydrogenation and phosphorization can be performed.
[0074] (Crystal Structure)
[0075] The magnetic compound according to the embodiment of the
invention is a rare earth element-containing magnetic compound
having a ThMn.sub.12 type tetragonal crystal structure shown in
FIG. 3. A lattice constant a of the crystal structure is within a
range of 0.850 nm to 0.875 nm, a lattice constant c of the crystal
structure is within a range of 0.480 nm to 0.505 nm, and a lattice
volume of the crystal structure is within a range of 0.351 nm.sup.3
to 0.387 nm.sup.3. Further, as shown in FIGS. 4A to 4C and 5A and
5B, hexagons A, B, and C are defined as follows: the hexagon A is
defined as a six-membered ring centering on a rare earth atom,
which is formed of Fe (8i) and Fe(8j) sites (FIGS. 4A and 5A); the
hexagon B is defined as a six-membered ring which includes Fe (8i)
and Fe(8j) sites in which Fe (8i)-Fe (8i) dumbbells form two sides
facing each other (FIGS. 4B and 5A); and the hexagon C is defined
as a six-membered ring which is formed of Fe (8j) and Fe(8f) sites
and whose center is positioned on a straight line connecting Fe
(8i) and a rare earth atom to each other (FIGS. 4C and 5B). At this
time, a length Hex (A) of the hexagon A in a direction of axis a is
shorter than 0.611 nm, an average distance between Fe (8i) and Fe
(8i) in the hexagon A is 0.254 nm to 0.288 nm, an average distance
between Fe (8j) and Fe (8j) in the hexagon B is 0.242 nm to 0.276
nm, and an average distance between Fe (8f) and Fe (8f) facing each
other with the center of the hexagon C interposed therebetween in
the hexagon C is 0.234 nm to 0.268 nm.
[0076] As shown in FIG. 6, as compared to in a magnetic compound of
the related art, in the magnetic compound according to the
embodiment of the invention, the amount of T (for example, Ti) as a
stable element is small, and the shape and dimension balance of the
hexagon A deteriorates when Ti having a large atomic radius is
substituted with Fe. However, this deterioration is compensated for
by Zr having a smaller atomic radius than Nd.
[0077] Further, the magnetic powder according to the embodiment of
the invention is represented by the formula
(R.sub.(1-x)Zr.sub.x).sub.a(Fe.sub.(1-y)Co.sub.y).sub.bT.sub.cM.sub.dA.su-
b.e and includes a ThMn.sub.12 type crystal structure, in which a
volume percentage of an .alpha.-(Fe,Co) phase is 20% or lower. In
the above-described formula, R represents one or more rare earth
elements, T represents one or more elements selected from the group
consisting of Ti, V, Mo, and W, M represents one or more elements
selected from the group consisting of unavoidable impurity
elements, Al, Cr, Cu, Ga, Ag, and Au, A represents one or more
elements selected from the group consisting of N, C, H, and P,
b=100-a-c-d, 0<c.ltoreq.7, 0.ltoreq.d.ltoreq.1, and
1.ltoreq.e.ltoreq.18.
Examples 1 to 5 and Comparative Examples 2 to 5
[0078] Molten alloys for preparing compounds having a composition
shown in FIG. 7 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. The quenched ribbon underwent a heat
treatment in an Ar atmosphere at 1200.degree. C. for 4 hours. Next,
in an Ar atmosphere, the ribbon was crushed using a cutter mill,
and particles having a particle size of 30 .mu.m to 75 .mu.m were
collected. From each of SEM images (backscattered electron images)
of the obtained particles, the size and area ratio of an
.alpha.-(Fe,Co) phase were measured, and a volume percentage was
calculated from the expression Area Ratio=Volume Percentage. Next,
the obtained particles were nitrided in nitrogen gas having a
purity of 99.99% at 450.degree. C. for 4 hours. The obtained
particles underwent magnetic characteristic evaluation (VSM) and
crystal structure analysis (XRD). Further, the volume percentage of
the .alpha.-(Fe,Co) phase after nitriding was calculated based on a
graph shown in FIG. 15, the graph showing a relationship between
the size of the .alpha.-(Fe,Co) phase in the sample before
nitriding and the volume percentage of the .alpha.-(Fe,Co) phase in
the sample after nitriding which were measured from the SEM image.
The results are shown in FIGS. 7, 8, and 9.
Comparative Example 1
[0079] Molten alloy for preparing a compound having a composition
shown in FIG. 7 below was prepared. The molten alloy was quenched
at a rate of 10.sup.4 K/sec using a strip casting method to prepare
a quenched ribbon. Next, in an Ar atmosphere, the alloy having
undergone hydrogen embrittlement was crushed using a cutter mill,
and particles having a particle size of 30 .mu.m or less were
collected. The obtained particles were press-formed in a magnetic
field, were sintered at 1050.degree. C. for 3 hours, and underwent
a heat treatment at 900.degree. C. for 1 hour and at 600.degree. C.
for 1 hour. The obtained magnet underwent magnetic characteristic
evaluation (VSM) and crystal structure analysis (XRD), and the
results are shown in FIGS. 7, 8, and 9.
[0080] As clearly seen from the results of FIGS. 7, 8, and 9, when
the Ti content was lower than 7 at %, saturation magnetization was
improved (in particular, at a high temperature), and higher
anisotropy field and higher saturation magnetization than those of
a NdFeB magnet were exhibited (Examples 1 to 5). An increase in
saturation magnetization caused by Co addition was observed, in
particular, at a high temperature (for comparison to Examples 1 and
2).
Examples 6 and 7
[0081] Molten alloys for preparing compounds having a composition
shown in FIG. 12 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. In Example 7, in an Ar atmosphere,
the quenched ribbon underwent a heat treatment at 1200.degree. C.
for 4 hours. Next, in an Ar atmosphere, the ribbon was crushed
using a cutter mill, and particles having a particle size of 30
.mu.m to 75 .mu.m were collected. Regarding each of the particles,
the size and area ratio of the .alpha.-(Fe,Co) phase were measured
and the volume percentage thereof was calculated using the same
method as in Example 1. Next, the obtained particles were nitrided
in nitrogen gas having a purity of 99.99% at 450.degree. C. for 4
hours. The obtained particles underwent magnetic characteristic
evaluation (VSM) and crystal structure analysis (XRD). Further, the
volume percentage of the .alpha.-(Fe,Co) phase after nitriding was
calculated using the same method as in Example 1. The results are
shown in FIGS. 10, 11, and 12.
Comparative Examples 6 to 10
[0082] Molten alloys for preparing compounds having a composition
shown in FIG. 12 below were prepared by arc melting. Each of the
molten alloys was quenched at a rate of 50 K/sec using a strip
casting method to prepare a quenched ribbon. In Comparative
Examples 7, 8 and 10, in an Ar atmosphere, the quenched ribbon
underwent a heat treatment at 1100.degree. C. for 4 hours. Next, in
an Ar atmosphere, the ribbon was crushed using a cutter mill, and
particles having a particle size of 30 .mu.m to 75 .mu.m were
collected. The obtained particles were nitrided in nitrogen gas
having a purity of 99.99% at 450.degree. C. for 4 hours. The
obtained particles underwent magnetic characteristic evaluation
(VSM) and crystal structure analysis (XRD), and the results thereof
are shown in FIGS. 10, 11, and 12 together with the measurement
results of the size and volume percentage of the .alpha.-(Fe,Co)
phase which were measured using the same method as in Example
1.
Comparative Examples 11 and 12
[0083] Molten alloys for preparing compounds having a composition
shown in FIG. 12 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. In Comparative Example 12, in an Ar
atmosphere, the quenched ribbon underwent a heat treatment at
1100.degree. C. for 4 hours. Next, in an Ar atmosphere, the ribbon
was crushed using a cutter mill, and particles having a particle
size of 30 .mu.m to 75 .mu.m were collected. The obtained particles
were nitrided in nitrogen gas having a purity of 99.99% at
450.degree. C. for 4 hours. The obtained particles underwent
magnetic characteristic evaluation (VSM) and crystal structure
analysis (XRD), and the results thereof are shown in FIGS. 10, 11,
and 12 together with the measurement results of the size and volume
percentage of the .alpha.-(Fe,Co) phase which were measured using
the same method as in Example 1.
[0084] FIG. 13 shows backscattered electron images of particles
obtained in Examples 6 and 7 and Comparative Example 8. In
Comparative Example 8 in which arc melting was performed, a large
amount of Fe was deposited and the structure was heterogeneous. On
the other hand, in Examples in which quenching was performed, the
segregation of the structure was not observed in EPMA. FIG. 14
shows the XRD results of the particles obtained in Examples 6 and 7
and Comparative Example 8. It was found that the peak intensities
of .alpha.-Fe became lower in order from Comparative Example 8 (arc
melting).fwdarw.Example 6 (quenching).fwdarw.Example 7
(quenching+homogenization heat treatment).
[0085] It is considered from the above results that, due to
quenching, the .alpha.-(Fe,Co) phase was refined, the amount
thereof deposited was reduced, and the entire structure was refined
and homogeneously dispersed; as a result, characteristics were
further improved. In addition, it is considered that, by further
performing the heat treatment after cooling, the homogenization of
the refined structure progressed, and the amount of the
.alpha.-(Fe,Co) phase was reduced; as a result, characteristics
were improved. In this way, even when the Ti content was reduced
from 7 at % to 4 at %, due to the quenching treatment and the
homogenization heat treatment, the deposition of the
.alpha.-(Fe,Co) phase was suppressed, and anisotropy field was
exhibited as in the related art. As a result, a magnetic compound
having a ThMn.sub.12 type crystal structure in which high
characteristics of anisotropy field and saturation magnetization
were realized was able to be prepared.
Examples 8 to 15 and Comparative Example 13
[0086] Molten alloys for preparing compounds having a composition
shown in FIG. 16 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. The quenched ribbon underwent a heat
treatment in an Ar atmosphere at 1200.degree. C. for 4 hours (a
cobalt content y in
Nd.sub.7.7(Fe.sub.(1-y)Co.sub.y).sub.86.1Ti.sub.6.2N.sub.7.7 was
changed). Next, in an Ar atmosphere, the ribbon was crushed using a
cutter mill, and particles having a particle size of 30 .mu.m or
less were collected. The obtained particles were nitrided in
nitrogen gas having a purity of 99.99% at 450.degree. C. for 4
hours to 24 hours. The obtained particles underwent magnetic
characteristic evaluation (VSM) and crystal structure analysis
(XRD). The results are shown in FIGS. 16 and 17 to 19.
[0087] As can be seen from the experiment results, anisotropy field
exhibits high values without being substantially affected by the Co
substitution ratio. On the other hand, saturation magnetization was
the maximum at Co substitution ratio=0.3 and decreased at y=0.7 or
higher. Further, the Curie point increased along with an increase
in Co content (when y=0.5 or higher, the Curie point was not able
to be measured due to the limitation of the apparatus).
Accordingly, it was found that a range of 0.ltoreq.y.ltoreq.0.7 is
preferable in regard to Co.
[0088] FIGS. 20 to 22 show relationships between a Co substitution
ratio and lattice constants a and c and a lattice volume V of a
crystal structure. From the above results, the following was found:
the lattice constant a of the crystal structure is within a range
of 0.850 nm to 0.875 nm, the lattice constant c of the crystal
structure is within a range of 0.480 nm to 0.505 nm, and the
lattice volume V of the crystal structure is within a range of
0.351 nm.sup.3 to 0.387 nm.sup.3.
[0089] FIGS. 23 and 24 show a relationship between anisotropy field
and saturation magnetization. In the samples of Examples according
to the embodiment of the invention, sufficiently high magnetic
characteristics were obtained.
[0090] Here, in the crystal structure, hexagons A, B, and C were
defined as follows: the hexagon A was defined as a six-membered
ring centering on a rare earth atom R, which is formed of Fe (8i)
and Fe(8j) sites; the hexagon B was defined as a six-membered ring
which included Fe (8i) and Fe(8j) sites in which Fe (8i)-Fe (8i)
dumbbells formed two sides facing each other; and the hexagon C was
defined as a six-membered ring which is formed of Fe (8j) and
Fe(8f) sites and whose center was positioned on a straight line
connecting Fe (8i) and a rare earth atom to each other. At this
time, it was found from FIG. 7 that a length Hex(A) of the hexagon
A in a direction of axis a was shorter than 0.611 nm which was a
value of a composition NdFe.sub.11TiN
(Nd.sub.7.7Fe.sub.92.3Ti.sub.7.7N.sub.7.7).
Example 16 and Comparative Examples 14 to 17
[0091] Molten alloys for preparing compounds having a composition
shown in FIG. 25 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. The quenched ribbon underwent a heat
treatment in an Ar atmosphere at 1200.degree. C. for 4 hours (a
titanium content c in
Nd.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.92.30-cTi.sub.cN.sub.7.7 was
changed). Next, in an Ar atmosphere, the ribbon was crushed using a
cutter mill, and particles having a particle size of 30 .mu.m or
less were collected. The obtained particles were nitrided in
nitrogen gas having a purity of 99.99% at 450.degree. C. for 4
hours. The obtained particles underwent magnetic characteristic
evaluation (VSM) and crystal structure analysis (XRD). The results
are shown in FIGS. 25 and 27.
[0092] It was found from the results of crystal structure analysis
using XRD in FIG. 27 that, when the Ti content was 5.8 at % or
higher, a 1-12 phase was formed. On the other hand, when the Ti
content was 3.8 at %, a 3-29 phase was formed, and when the Ti
content was 1.9 at % or lower, a 2-17 phase was formed. In
addition, FIG. 26 below shows a relationship between a change in Ti
content and a change in crystal structure.
Example 17 to 27 and Comparative Examples 18 to 31
[0093] Molten alloys for preparing compounds having a composition
shown in FIGS. 28 and 29 below were prepared. Each of the molten
alloys was quenched at a rate of 10.sup.4 K/sec using a strip
casting method to prepare a quenched ribbon. The quenched ribbon
underwent a heat treatment in an Ar atmosphere at 1200.degree. C.
for 4 hours (a ratio x of Zr substitution and a titanium content c
in
(Nd.sub.(7.7-x)Zr.sub.x)Fe.sub.0.75Co.sub.0.25).sub.92.30-cTi.sub.cN.sub.-
7.7 were changed). Next, in an Ar atmosphere, the ribbon was
crushed using a cutter mill, and particles having a particle size
of 30 .mu.m or less were collected. The obtained particles were
nitrided in nitrogen gas having a purity of 99.99% at 450.degree.
C. for 4 hours to 16 hours. The obtained particles underwent
magnetic characteristic evaluation (VSM) and crystal structure
analysis (XRD). The results are shown in FIGS. 28, 29, and 30.
[0094] It was found from the results of FIGS. 28 and 29 that the
ability to form the 1-12 phase decreases along with a decrease in
Ti content and is improved along with an increase in Zr addition
amount. It was clearly found from the results of FIG. 30 that, in a
region where the 1-12 phase can be formed, a relationship between
the ratio of Zr substitution x and the Ti content c satisfies a
region (0<c<7, x.gtoreq.0) surrounded by c>-38x+3.8 and
c>6.3x+0.65. The reason for this is presumed to be as follows.
As shown in FIG. 6, when the Ti content was reduced, Ti atoms in
the 8i site of hexagon A are substituted with Fe atoms having a
small atomic radius, and thus the size balance of the hexagon A is
decreased. Therefore, the 1-12 phase is not stably formed. However,
the size balance is compensated for by substitution of Zr atoms
having a smaller atomic radius than Nd atoms. As a result, the 1-12
phase can be formed irrespective of a decrease in Ti content.
Examples 28 to 33 and Comparative Examples 32 to 33
[0095] Molten alloys for preparing compounds having a composition
shown in FIG. 31 below were prepared. Each of the molten alloys was
quenched at a rate of 10.sup.4 K/sec using a strip casting method
to prepare a quenched ribbon. The quenched ribbon underwent a heat
treatment in an Ar atmosphere at 1200.degree. C. for 4 hours. Next,
in an Ar atmosphere, the ribbon was crushed using a cutter mill,
and particles having a particle size of 30 .mu.m or less were
collected. The obtained particles were nitrided in nitrogen gas
having a purity of 99.99% at 450.degree. C. for 4 hours (a nitrogen
content e was changed in
Nd.sub.7.7(Fe.sub.0.75Co.sub.0.25).sub.86.5Ti.sub.5.8N.sub.e and
Nd.sub.7.7Fe.sub.86.5Ti.sub.5.8N.sub.e). The obtained particles
underwent magnetic characteristic evaluation (VSM) and crystal
structure analysis (XRD). The results are shown in FIGS. 31 to
34.
[0096] It was found that the lattice constant was increased in
directions of axes a and c along with an increase in N content. In
addition, it was found that nitrogen was introduced in amount of up
to 15.4 at % without breaking the crystal structure. It was found
as described above that saturation magnetization and anisotropy
field were increased along with an increase in N content.
* * * * *